1. Field of the Invention
The present invention relates to a multicolor ink set suitable for an ink jet recording method, and an ink jet recording method using the multicolor ink set.
2. Description of Related Art
A printer using an ink jet method in which liquid or molten solid ink is discharged through a nozzle, slit or porous film to effect recording on paper, cloth, film and the like has various merits such as small size, low cost, silence and the like. Black and white or fullcolor printers of the ink jet type are widely commercially available. Among them, the piezo ink jet method which uses a piezo-electric element or a thermal ink jet method in which a liquid drop is formed by the action of thermal energy so that recording is conducted has a lot of merits. For example, high speed printing is realized, high resolution is obtained, and the like.
For coloration in the ink jet recording method, inks such as black, cyan, magenta, yellow ink and the like are generally used, and these inks are required to have a lot of properties so that (1) a clear image is obtained on any type of paper without blotting of either primary or secondary colors, (2) a black letter image is clear and has no blotting, (3) storage stability of an image, particularly, water resistance and light resistance of an image is excellent, (4) fixation ability of an image is good, (5) there is no blotting between different colors on any paper, (6) there is no void or deletion in an image, and the like.
To satisfy these required various ink properties, a lot of ideas have been suggested, and carried out. For example, Japanese Patent Application Laid-Open (JP-A) No. 3-122,171, U.S. Pat. Nos. 5,185,034; 5,145,519; 5,273,573; 5,143,547 and the like report that excellent tone is obtained on exclusive coated paper for ink jet recording by combining specific dyes.
However, in this case, there are problems that tone is not sufficient on normal paper, or in particular, a black letter image is not clear, color reproducibility on an OHP sheet is not excellent, water resistance and light resistance of an image are not sufficient, and the like.
A lot of ideas have been suggested and carried out for improving storage stability of an image, in particular, water resistance in the ink jet recording method. For example, there is used a so-called "highly waterfastness dye" which is a dye using a carboxyl group as a hydrophilic group of a water-soluble dye. However, in this case, there is a problem that when a black ink mainly used for printing letters is wet, the letters become illegible, namely, the waterfastness of the black ink is still insufficient.
Therefore, use of a pigment as a coloring agent has been suggested. However, in this case, though approximately sufficient water resistance and light resistance are obtained, there are problems regarding reliability. A clear image can not be obtained especially a color image, clogging easily occurs in the point of a print nozzle and consequently a void or deletion in an image is easily caused, fixation ability of an image is poor, and the like.
On the other hand, there is also commercially available an ink jet recording apparatus using a multicolor ink set comprising only black ink in the form of pigment dispersed ink for obtaining a clear image and color ink in the form of dye ink. To use black ink in the form of pigment dispersed ink is very effective for improving water resistance and image quality. However, in this case, fixation ability onto a recording material such as paper, film and the like is problematical.
When a component which acts as a binder is added to ink for improving this fixing ability, clogging easily occurs. Therefore, the component can not be added in an amount sufficient to largely improve fixing ability. On the other hand, when ink is fully impregnated into paper, fixing ability is improved, but, there occur problems such as image concentration decreases, image blotting increases, and the like.
In the case of black ink, the surface tension is set at high level and the ink is designed so that impregnation into paper requires 10 seconds or more in view of prevention of expansion of an image and blotting, since the black ink is often used for printing letter images. There is a problem that if a full-color image is recorded using such a black ink, blotting occurs between different colors. This is more marked with normal paper. Therefore, a lot of ideas have been conventionally suggested. For example, U.S. Pat. No. 5,198,023 suggests preventing blotting between colors by combining black ink containing an anionic dye, and yellow ink containing a cationic dye and a polyvalent coagulant.
However, in this case, long term ink shelf life is problematical, and in a thermal ink jet method, burnt deposition on a heater, so-called kogation is a problem.
Further, Japanese Patent Application Laid-Open (JP-A) No. 7-47762 suggests a method in which when ink having quick penetration ability into paper and ink having slow penetration ability into paper are printed at the same position in order to reduce blotting between colors. However, in the case of this method, there is a problem that recording of an image takes a long time and increased printing speed can not be accomplished. Another method is suggested in which paper is heated by a heater. However, in this case, such problems as electric power consumption increases which result in cost rises, and the like arise. However, in these cases, excellent effects are not easily obtained by methods in which color ink dye concentrations are set to about 0.1 to 2.0% by weight and gradation properties are obtained by overprinting for the purpose of providing an image having a level of quality corresponding to that of a photograph. Namely, blotting into an image having different color becomes significant where a high volume of ink is printed per unit area in image parts adjacent to black ink. Therefore, undesirable results occur.